Manufacture of ophthalmic lenses by excimer laser

ABSTRACT

Complex small objects such as ophthalmic lenses are quickly and accurately fabricated from plastic or glass blanks of ablatable material such as plastic or glass by cutting, shaping, and radiusing the blank entirely by laser light, using appropriate masks and focusing optics.

FIELD OF THE INVENTION

This invention relates to the manufacture of ophthalmic lenses such as a contact, corneal implant, and intraocular lenses, or of other small plastic or glass objects of similar shape, and more particularly to a method of making such lenses or objects with a high degree of precision at low cost by using an excimer laser.

BACKGROUND OF THE INVENTION

Ophthalmic lenses are normally manufactured by a mechanical process in which a block of polymethylmethacrylate (PMMA) is machined while being adhesively held on a support. The machining is quite difficult because of the small size of the lens and the intricacy of the shape into which the lens must be machined.

Typically, three operations must be performed to shape a lens:

(1) the workpiece must be cut out from a blank to form, e.g., an integral optic and haptic;

(2) the surface of the workpiece must be machined to the desired optical specifications (which may include convexities or concavities of varying radii at different points on the surface of the lens; and

(3) the edges of the workpiece must be radiused or rounded.

In the prior art, the edge rounding step alone typically required 7-14 days of gemstone tumbling, and precision was hard to accomplish in all of the steps.

SUMMARY OF THE INVENTION

The present invention provides a method of fabricating ophthalmic lenses or similar small objects quickly and accurately by using a laser, and particularly an excimer laser, to cut, surface-model and bevel a workpiece which is preferably made of PMMA but may, for appropriate purposes, be made of other plastics or of glass. The type and tuning of the laser is dependent upon the material of the blank.

In accordance with the invention, the workpiece is first cut to shape by shining a laser beam through a mask outlining the form of the cut required to shape (in the case of an ophthalmic lens) the optic and haptic. Considerable precision can be obtained in this step by expanding the laser beam in front of the mask and then reducing it beyond the mask to provide fine detail from a relatively large mask. The depth of the cut can be controlled by the number and energy of the pulses.

The surface modeling of the lens is next achieved by masking a laser beam in such a way that its energy distribution varies across the surface of the workpiece so as to ablate it to differing degrees at different points of the surface. This can be achieved by using a mask of varying opacity or a semi-transparent mirror with a coating of varying thickness at different points on the surface. This step, if desired, may be performed before the cutting step.

Finally, a laser beam is masked and focused generally into the form of a hollow cone whose tip is the focal point of the beam. By exposing the workpiece to the beam on one side of the focal point and then on the other, two bevel cuts are made along the perimeter of the upper and lower surfaces, respectively, of the workpiece. When combined with a vertical section of the side of the workpiece, these bevel cuts form an approximation of a rounded edge which is further softened by the slight melting of the workpiece material produced by the heat generated by the laser during cutting.

It is therefore the object of the invention to quickly and accurately produce a complex small object such as an ophthalmic lens from a blank entirely by the use of a laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an intraocular lens to be manufactured by the method of this invention;

FIG. 2 is a schematic diagram of a laser optic used in the cutting step of the invention;

FIG. 3 is a plan view of the mask used in the cutting step;

FIG. 4 is a schematic diagram illustrating the surface modeling step of this invention;

FIG. 5 is a plan view of the mask used in the surface modeling step;

FIG. 6 is a schematic diagram illustrating the edge beveling step of this invention;

FIG. 7 is a plan view of the mask used in the beveling step;

FIG. 8 is a fragmentary detail section of the workpiece after the first beveling step; and

FIG. 9 is a fragmentary detail section of the workpiece after the second beveling step.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment of the invention, which is the manufacture of ophthalmic lenses from a PMMA blank, the method of this invention is carried out with an excimer laser, i.e. a laser operating in the high ultraviolet wavelengths. An argon-fluoride laser operating at a wavelength of 193 nm in 250 millijoule pulses is preferred, but broadly any ultraviolet wavelength substantially absorbed by the material of the workpiece may be used. The choice of the laser is dictated by its ability to break up the large molecules of the workpiece material (as in the case of plastic) or to melt the material (as in the case of glass) so that the material will ablate.

FIG. 1 shows a typical intraocular lens which may be produced by the method of this invention. The workpiece 10 has an optic 12 which forms the actual lens, and a haptic 14 by which the lens is anchored in the patient's eye. In the prior art, polypropylene is usually used for the haptic 14, and PMMA is used for the optic 12. However, both the optic 12 and the haptic 14 may be formed of PMMA, and in the process of this invention this is preferable because the entire workpiece can be cut as a single piece. Of course, other ultraviolet-absorbing materials than PMMA (e.g. silicone) may be used for the workpiece if they are medically acceptable and properly ablatable.

FIG. 2 shows an arrangement useful in cutting the workpiece 10 from a block of PMMA. An excimer laser 16 emits a beam 18 of coherent ultraviolet light. Because the diameter of beam 18 is fairly small, a conventional laser beam expander 20 is used to expand the beam 18 to a diameter of several centimeters. A mask 22 best shown in FIG. 3 is formed integrally with the beam expander 20 or placed into the path of the expanded beam 18 to allow only a narrow strip of light in the shape of the outline 24 of the workpiece 10 to pass through the mask 22.

A beam converger or focusing optic 26 is used to project a reduced image of the outline 24 onto the PMMA block 28. Repeated pulses of the laser 16 will ablate the material of the block 28 until the profiled lens or workpiece 10 is very precisely cut out of the block 28. The precision of the cut is enhanced (and the power density of the beam increased) by the use of a relatively large mask 22 and a substantial reduction of the mask image on the block 28.

After being cut out from the block 28, the workpiece 10 is placed into the path of an excimer laser beam 30 (FIG. 4) which has a uniform energy distribution across its area. A mask 32 is interposed between the workpiece 10 and beam 32.

As best shown in FIG. 5, the mask 32 has different degrees of transparency at different points on the mask 32. For example, the mask 32 may have a coating of variable transmission characteristics, or it may be a neutral density filter (such as a polarizing or haze filter) with non-uniform transmission characteristic. In any event, the mask 32 transmits a large amount of beam energy in the areas 34 corresponding to desired depressions in the workpiece 10, and a small amount in the areas 36 corresponding to desired protrusions in the workpiece 10.

By appropriately controlling the transmission characteristics of the mask 32, it is possible to model or shape the surface 38 of the workpiece 10 in any desired manner without complex machining, and to do so precisely in a small amount of time.

In an alternative embodiment of the invention, the mask 32 may take the form of a semi-transparent mirror with a reflective coating whose thickness varies along its surface. In that embodiment, the laser energy not used for ablation is reflected away from the workpiece.

After the shaping or modeling step of FIGS. 4 and 5, the workpiece is fully formed but has sharp vertical edges which are not suitable for intraocular use. In the prior art, the edges of the workpiece were radiused or rounded by gemstone tumbling for 7-14 days, but besides being time-consuming, this prior art method often defeated the carefully achieved precision of the workpiece.

In accordance with the invention, an excimer laser beam 40 (FIG. 6) is expanded by a beam expander or (preferably) by a pair of curved mirrors 42, 44. The use of reflective rather than refractive beam expanding optics is preferred because it permits higher power transfer with smaller optics while avoiding damage to the optics.

The expanded beam 46 is conducted through a mask 48 best shown in FIG. 7 to a focusing lens 50. As a result, a beam generally in the form of a hollow cone is produced, with the tip of the cone being the focal point 52.

In order to round its edges, the workpiece 10 is first positioned below the focal point 52 at 54, and the laser is turned on. The conical shape of the beam will produce a bevel 56 (FIG. 8) on the edges of the workpiece 10. The ends of the bevel 56 are slightly rounded at 58, 60 by the small amount of heat which is produced during the ablation of workpiece material which forms the bevel 56.

When the bevel 56 has been fully formed, the workpiece 10 is positioned above the focal point 52 at 62, and the beam is turned on again. This time, the conical shape of the beam results in cutting a bevel 64 (FIG. 9) whose edges are slightly rounded at 66, 68 for the same reason as described above.

When combined with the vertical surface 70, the bevels 56, 64 and their rounded extremities provide a sufficient approximation of a rounded edge for the workpiece 10 to make it suitable for implantation in a patient's eye without danger of irritation.

It will be seen that the above-described process provides a fast and accurate way of manufacturing intraocular lenses without the use of complex machining equipment. The invention can, of course, be carried out with variations: for example, a very narrow laser beam may be moved around the periphery of the workpiece in the cutting and beveling steps, rather than cutting or beveling the entire periphery at once; or a mask may be scanned rather than being exposed all at once. 

We claim:
 1. A method of making small objects from a blank of ablatable material, comprising the steps of:cutting a workpiece from said blank by exposing said blank to laser light in the outline of said workpiece without focusing the laser light at the workpiece; exposing the surface of said workpiece to laser light through a mask having areas transmitting said light in varying degrees; and beveling the edges of said workpiece by exposing them to an inclined beam of laser light.
 2. The method of claim 1, in which said laser light is in the ultraviolet range.
 3. The method of claim 1, in which said material is plastic.
 4. The method of claim 3, in which said material is polymethylmethacrylate.
 5. The method of claim 1, in which said material is glass.
 6. The method of claim 1, in which said workpiece is an ophthalmic lens having an optic and a haptic formed as a single piece.
 7. The method of shaping the edges of a workpiece formed of an ablatable material, comprising the steps of:providing an excimer laser beam; masking said beam to obscure the center thereof but leave a peripheral portion thereof unobscured; deflecting said peripheral portion toward a focus; positioning a workpiece at one point of time spaced from the focus in such a manner that said peripheral portion intersects an edge portion of said workpiece at an angle; and causing said beam to have sufficient power to ablatively photodecompose said workpiece in its path.
 8. The method of claim 7, in which said masking step includes the step of producing a peripheral portion of substantially annular shape.
 9. A method comprising:directing laser energy through a mask without focusing the laser energy at the mask and with the mask having variable transmissivity characteristics to the laser energy to provide a first laser beam of variable energy across its width; and directing the laser beam of variable energy against a surface of a workpiece for a sufficient time to remove material from multiple locations on the surface of the workpiece in accordance with said characteristics with more of the material being removed at one of the locations than is removed at another of the locations.
 10. A method as defined in claim 9 wherein the surface generally faces in the direction from which the laser energy is directed.
 11. A method as defined in claim 9 wherein said step of directing the laser beam of variable energy against the surface of the workpiece to shape the surface is carried out to shape the surface of the workpiece into an ophthalmic lens.
 12. A method as defined in claim 9 wherein the laser energy is excimer laser energy.
 13. A method as defined in claim 9 including cutting the workpiece from a blank by exposing the blank to laser energy in the outline of said workpiece.
 14. A method as defined in claim 13 including beveling an edge of the workpiece by exposing it to laser energy.
 15. A method as defined in claim 9 including directing a second laser beam toward a blank in a pattern without focusing the second laser beam at the blank for a sufficient length of time to cut the workpiece from the blank.
 16. A method as defined in claim 15 wherein the step of directing the second laser beam toward the blank includes directing the second laser beam through a mask with the second laser beam passing through the mask being in said pattern.
 17. A method as defined in claim 15 wherein the laser energy is directed toward the blank to cut the workpiece from the blank without relatively moving the workpiece and the pattern.
 18. A method as defined in claim 15 including directing laser energy through a mask to the workpiece without focusing the laser energy at the workpiece to bevel an edge of the workpiece.
 19. A method as defined in claim 9 including beveling an edge of the workpiece by exposing it to laser energy.
 20. A method as defined in claim 9 including directing laser energy through a mask to the workpiece without focusing the laser energy at the workpiece to bevel an edge of the workpiece.
 21. A method as defined in claim 9 wherein said step of directing the laser beam of variable energy is carried out without relatively moving the laser beam and the workpiece.
 22. A method comprising:directing laser energy through a mask toward an object without focusing the laser energy on the mask or the object and with the laser energy passing through the mask being in a pattern and exposing the object to the laser energy for a sufficient length of time to allow the laser energy to cut a workpiece having the shape of said pattern from the object.
 23. A method as defined in claim 22 wherein the laser energy is directed toward the object to cut the workpiece from the object without relatively moving the object and the pattern.
 24. A method as defined in claim 22 including beveling an edge of the workpiece by exposing it to laser energy.
 25. A method as defined in claim 22 including directing laser energy through a mask to the workpiece without focusing the laser energy at the workpiece to bevel an edge of the workpiece.
 26. A method as defined in claim 22 wherein said pattern is generally in the shape of an intraocular lens.
 27. A method comprising:directing laser energy in a pattern toward an object without focusing the laser energy on the object and exposing the object to the laser energy for a sufficient length of time to allow the laser energy to bevel an edge of the object.
 28. A method as defined in claim 27 wherein the laser energy is directed toward the object to bevel the edge of the object without relatively moving the object and the pattern.
 29. A method as defined in claim 27 wherein the step of directing includes directing the laser energy to a focus which is spaced from the object.
 30. A method as defined in claim 27 wherein the step of directing includes directing the laser energy through a mask to the object without focusing the laser energy at the mask.
 31. A method comprising:directing laser energy through a mask without focusing the laser energy at the mask and with the mask having variable reflective characteristics to the laser energy to provide a first laser beam of variable energy across its width; and directing the laser beam of variable energy against a surface of a workpiece for a sufficient time to remove material from multiple locations on the surface of the workpiece in accordance with said characteristics with more of the material being removed at one of the locations than is removed at another of the locations.
 32. A method as defined in claim 31 wherein said step of directing the laser beam of variable energy is carried out without relatively moving the laser beam and the workpiece.
 33. A method as defined in claim 31 including cutting the workpiece from a blank by exposing the blank to laser energy in the outline of said workpiece.
 34. A method as defined in claim 31 including beveling an edge of the workpiece by exposing it to laser energy. 